1. Technical Field
The present invention relates to a device and a method for the detection of hydrogen in a gas volume.
2. Discussion
Today, hydrogen is commercially used as an energy source in a broad field of applications. It is known for instance to operate fuel cells with hydrogen. It is also known to operate combustion engines with hydrogen. But hydrogen involves a risk of ignitable air/hydrogen mixtures being formed in the case of possible leakages of hydrogen-carrying passages or systems. The explosive limit for air/hydrogen mixtures ranges from 4 to 75% by volume. Such ignitable or explosive air/hydrogen mixtures are also named oxyhydrogen gas.
Hydrogen is a colourless, odourless and flavourless gas, which fact makes it difficult or even impossible to perceive hydrogen by human senses.
Regarding the calorific value of pure hydrogen of 13 MJ/m3, leakages in hydrogen-carrying systems constitute an immense risk potential in the operation of hydrogen plants.
Hydrogen is also produced in energy stores like accumulators, especially during the charging operation. Explosive air/hydrogen mixtures may be generated in this case, too.
For the safe operation of hydrogen plants or energy stores like accumulators it is therefore necessary to securely determine the formation of ignitable air/hydrogen mixtures, in order to be able to initiate appropriate counter measures such as venting the room or interrupting the hydrogen supply.
Up to present, hydrogen is detected in prior art by means of electrochemical sensors having a two- or three-electrode device (working electrode, reference electrode and counter electrode) (example: U.S. Pat. No. 7,060,169). The sensors include a hydrogen-permeable diaphragm and are used for measurements within a concentration range lower than 5% by volume. A disadvantage of electrochemical sensors is the sensitivity which decreases over the time (aging effect). This effect is caused by the degradation of the electrolyte as well as by side reactions on the electrodes. A shortening of the service time must be expected also in the case of an over-saturation of the electrolyte when the hydrogen concentrations are very high. In the presence of high water steam concentrations corrosion on the electronics and/or the blocking of the diaphragm accompanied by a clear deceleration of the response time may occur due to the formation of condensate.
A further principle for hydrogen detection makes use of a metal thin-film (e.g. Pd), where the measuring principle is based on a change of conductivity (EP 768528) or a change of light transmission (EP 1521080) of this metal thin-film due to the incorporation of hydrogen. These methods also display a reduction of the sensitivity in case of a water condensate formation as well as through carbon monoxide absorption. With hydrogen-containing gases like NH3 and H2S a reduction of the sensing capability occurs through a reduction of the selectivity of the sensor.
A further established method for measuring hydrogen in a broad concentration range is supported on the clearly lower conductivity of hydrogen compared to other gases. A drawback of this method however is the low selectivity resulting in faulty results in cases where hydrogen-containing gases are detected which include further gas components.